Polyisocyanate compositions obtained from aliphatic diisocyanates including 1,6-diisocyanatohexane (hereinafter, sometimes referred to as HDI; hexamethylene diisocyanate) and having an isocyanurate structure are excellent in weatherability and heat resistance, and accordingly have been widely used in various applications.
Recently, because of growing interest in global environmental protection, technology development has been actively performed toward the lowering of the viscosity of polyisocyanate used as a curing agent (for example, see Patent Literature 1). This is because the lowering of the viscosities of polyisocyanates allows the amounts of the organic solvents used in coating compositions to be reduced.
In this connection, various techniques have been disclosed on the techniques for lowering the viscosities of various polyisocyanates derived from, for example, aliphatic diisocyanates including HDI. From such techniques, here is quoted, for example, a technique related to a low viscosity polyisocyanate having a uretdione group (for example, see Patent Literature 2).
Additionally, there has been proposed a polyisocyanate composition excellent in curability and storage stability in spite of having a uretdione group (for example, see Patent Literature 3).
Moreover, as a technique to improve the stability in a state of being brought into contact with humidity, there has been disclosed a technique for adding a phosphorus-based compound such as an acidic phosphoric acid compound or an acidic phosphoric acid ester to an isocyanurate-type polyisocyanate (for example, see Patent Literature 4).